Device for damping the noise produced by a gas jet escaping from a duct

ABSTRACT

A device for damping the noise produced by a jet escaping from a duct in particular a jet engine nozzle, including silencer elements that are movable by control devices to project into the jet for silencing and retractable out of the jet for normal thrust, wherein, for reducing load on the control devices, means are provided for assisting movement of the silencer elements from their silencing position to their retracted position.

United States Patent Camboulives et a1.

[ 1 Aug. 29, 1972 [54] DEVICE FOR DAMPING THE NOISE PRODUCED BY- A GASJET ESCAPING FROM A DUCT Inventors: AndreAlplnmeMederlcLecuCam-Assignee:

Filed:

boullves, Billancourt; Jem-Clnude Lucien Deluge, Moissy-Cmmayel;'lheoplile M Le Mneut, Cesson; Roger Alli-ed Jules VendemmmckeAntonjllof France SodeteNatlomled'EtudeetdeCoustruction de Muteun dAviaflon,Paris,France May 3, 1911 Appl. No.2 139,146

FurdguAppllcaflonPrlorltyDuta May 11, 1970 US. Int.

France ..7017065 ..l8l/33 KG, 181/33 R1), 181/51,

33/06, FOln 1/14, mln 1/16 FieldolSeurchJSl/Si! R, 33 H, 33 HA, 33 HB,

181/33 HC, 33 HD, 43, 51, 64, 65;

[ References Cited UNITED STATES PATENTS 3,346,193 10/1967 'nnn'cl jgig/2 5,17 3,386,658 6/1968 Mehr ..239/127.3 3,420,442 1/1969 Teagle..239/127.3 3,587,973 6/1971 Wolf et a1. 1 81/51 X 2,682,147 6/1954Ferris ..239/127.3 3,289,945 1211966 Noren ..239l26$.19 3,432,100 3/1969Hardy et al. ............239/ 127.3 3,543,877 12/1970 Ranvier et a]..........239/ 127.3

Primary Examiner-Robert S. Ward, Jr. Attorney-William J. Daniel ABSTRACTA device for damping the noise produced by a jet escaping from a duct inparticular a jet engine norzle, including silencer elements that aremovable by control devices to project into the jet for silencing andretractable out of the jet for normal thrust, wherein, for reducing loadon the control devices, means are provided for assisting movement of thesilencer elements from their silencing position to their retractedposition.

PATENTEnAus 29 1912 SHEET CIROF 1O PATENTEBmszs I972 SHEEI UBUF 10PATENTEU Al" 2 9 I97? SHEET 07 0F 10 PAIliuTimuczs I972 SHEET OS [If 10PATENTEDnuszs m2 SHEET IOUF 10 DEVICE FOR DAMPING THE NOISE PRODUCED B AGAS JET ESCAPING FROM A DUCT This invention relates to a device fordamping the noise produced by a gas jet escaping from a duct such as ajet pipe or nozzle, of the kind which comprises, distributed about thejet whose noise is to be damped, a plurality of silencer elements eachof which comprises, carried by a holder or supporting element which canbe actuated under the action of a control device, a silencer element orscoop which can be moved, under the action of said control device,between an operative position in which it projects with negativeincidence into said jet, and an inoperative position in which it isretracted from said jet.

The invention relates more particularly although not exclusively to thedamping of the noise produced in operation by the propulsion jetescaping from the nozzle system of a jet engine fitted to an airbornevehicle such as an aircraft, in particular at the time of take-off andclimb-out.

In their operative position, the silencer elements exert a "peeling"effect upon the jet, which results in the separation, partially at anyrate, of the peripheral layer from the central part or core of the jet,this contributing, as those skilled in the art will appreciate, toimproved mixing between the gas of the jet and the environment,generally speaking air, which surrounds it, and thus to attenuation ofthe noise emitted by the jet. In their inoperative position, thesilencer elements are retracted away from the jet, so that there is noloss of thrust.

The introduction of a silencer of this type meets with certaindifficulties, however, from the point of view of the control of thesilencer elements. As those skilled in the art will appreciate, becausethe silencer elements project into the jet at a negative angle ofincidence, the lift produced by the jet upon the silencer elements islikewise negative. In other words, under the action of the aerodynamicforces to which they are subjected, the silencer elements, when in theoperative position, tend to penetrate further into the core of the jet.The result is that to keep them in silencer operative position and toretract them from their operative position into the inoperative positioninvolves overcoming the action of the jet, and this means that in orderto control them, control devices (in particular jacks) which are capableof developing substantial forces and are therefore heavy, bulky andexpensive, are required.

The object of the invention is to reduce these drawbacks, at least to asubstantial extent.

in accordance with a first aspect of the invention, in certain at leastof the silencer elements, the silencer element is arranged to pivotfreely on its holder element about an axis which divides said silencerelement, when considered in its operative position, into two sections,an upstream one and a downstream one, such that the center of pressureof silencer element is located in its downstream section, with theresult that the said silencer element is subjected to a thrust tendingto pivot it about said axis in a manner such as to reduce its angle ofincidence, considered in absolute terms, in the jet, said holder elementhaving a portion which forms a stop designed to cooperate with acorresponding mating portion integral with said silencer element, thusto limit the pivoting motion of said silencer element about said axis insaid direction.

The result of this arrangement is that on passage from its inoperativeposition to its operative position or vice versa, the silencer elemententers or leaves the jet with its downstream section; that in certain atleast of its intermediate positions it is free to align itself with thestreamlines of the jet flow; and that in the operative position itadopts in the jet an orientation such that the peeling efiect isproduced. When, the silencer element is aligned with the jetstreamlines, its lift is substantially zero, and this means aconsiderable reduction in the force exerted at the control deviceassociated with said silencer element.

In accordance with another aspect of the invention which could,furthermore, be applied independently of the first, the holder orsupport element is articulated to a fixed structure and is actuatedthrough the medium of a toggle mechanism with two segments which arearticulated on the one hand to one another and on the other handrespectively to said fixed structure and said holder element, saidtoggle mechanism, when the holder element occupies a positioncorresponding to the operative position of the silencer element,exhibiting a configuration such that the two articulated sections aredisposed in extension of one another.

In this arrangement, the two sections operate in the tensile mode,transmitting directly to the fixed structure the whole of the force towhich the silencer element is subjected. The control device or jackassoci'ated with the latter is then not subjected to these loads.

In accordance with another aspect of the invention, which can be appliedindependently of the foregoing aspects, a silencer element can beassociated with means for elastically biasing said element towards itsinoperative position, said means reinforcing the action the normalcontrol device which acts upon the holder element of the silencerelement.

In the case where said holder element is articulated to a fixedstructure about a pivot axis, said biasing means can advantageouslycomprise an element such as a section of cable which is subjected toelastic torsional loading about said axis.

This arrangement has the advantage that at all times it enables thesilencer element to be returned to the inoperative position, even if theaforesaid normal control device should fail.

The invention likewise relates to propulsion nozzles, in particular inturbojet (gas turbine jet) engines, which are equipped with an improvedsilencer of the aforedescribed kind. In the case where the nozzle is ofthe dual-flow or by-pass type, comprising a primary nozzle through whichthe jet, whose noise is to be damped, is discharged, and a secondaryfairing of larger cross-sectional area than the primary nozzle, saidfairing extending downstream beyond the nozzle exit orifice, thesilencer elements or scoops, and their holder elements, canadvantageously be designed so that in the inoperative position theyretract into said fairing.

The description which now follows and which relates to the accompanyingdrawing will indicate by way of example how the invention may be carriedinto practice.

[n the drawings FIG. 1 is a schematic longitudinal half-section througha propulsion nozzle equipped with a known type of silencer usingsilencer elements of the deflector or scoop type;

FIG. 2 is a schematic longitudinal half-section through a portion of apropulsion nozzle equipped with silencer elements of the deflector orscoop type, in accordance with a first embodiment of the invention, thesilencer elements being shown in the operative configuration;

FIG. 2a is a view similar to that of FIG. 2, this time, however, withthe silencer elements in the inoperative configuration;

FIG. 3 is an end elevation, taken in the direction of the arrow III ofFIG 2, of the silencer, with the nozzle lifted away;

FIGS. 4, 5, 6, 7 are sectional views of the silencer, respectively onthe lines lV-IV, V-V, VI-VI and VII-VII of FIG. 2;

FIG. 8 is a schematic longitudinal half-section of a portion of apropulsion nozzle equipped with silencer elements of the deflector orscoop type, in accordance with a second embodiment of the invention, thesilencer elements being shown in the inoperative configuration;

FIG. 8a is a view similar to that of FIG. 8, this time however with thesilencer elements in the operative configuration;

FIG. 9 is a developed plan view, partially sectioned and cut away, ofthe device shown in FIG. 8;

FIG. 10 is a sectional view on the line X-X of the device shown in FIG.8;

FIG. I1 is a sectional view on the line XI-XI of the device shown inFIG. 8;

FIG. 12 is a sectional view on the line XII-XI] of the device shown inFIG. 8a.

In FIG. 1, a propulsion nozzle, which constitutes the rear terminal partof a jet engine, has been illustrated. As is often the case inhigh-thrust jet engines, such as those installed in certain kinds ofsupersonic aircraft, said nozzle is of the dual-flow or by-pass type,with a primary nozzle 1 of fixed or variable exit section 2, and asecondary fairing 3 located coaxially about the primary nozzle andextending beyond the exit section thereof in the downstream direction.The fairing 3 is delimited externally by a wall 4 and internally by aconvergentdivergent wall 5 the throat and divergent portion of whichhave been respectively marked 6 and 7. Control flaps 8 articulated at 9may possibly be used to extend said fairing towards the rear. Theseflaps may be designed to operate automatically or may be under pilotcontrol. The walls 4 and 5 delimit between them a fixed box structureI0.

In operation, the hot gases which leave the primary nozzle 1, stillunder fairly high pressure, in the direction of the arrows f, form anoisy jet the boundary of which has been marked by the reference 11. Theannular space 12, defined between the internal wall of the secondaryfairing and the external wall of the primary nozzle followed by theboundary ll of the primary jet, passes a secondary airflow indicated bythe arrow F.

A known type of silencer which will effectively damp the noise emanatingfrom the jet f, comprises, distributed uniformly around the jet, aplurality of silencer elements each of which comprises a deflectorelement or scoop 13 carried by a holder element 14. The latter isconstituted by a bellcrank articulated at its angle about a pivot 15carried by a yoke 16 attached to the fixed structure of the fairing. Theshorter arm of the bellcrank is itself articulated at its end 17 to theend of the rod 18 of an actuater 19 such as a jack, housed in the boxstructure 10 and articulated at 20 to the fixed structure of thefairing.

Under the action of the jacks 19, the silencer elements 13 can be movedbetween two terminal positions respectively indicated in broken line andfull line, one being operative or silencing position and the other theinoperative or cruising position. Electrical limit contacts 21, 22provide the pilot with an indication that the silencer elements havereached one or the other of said positions. In the operative positionpressure is maintained in the jacks.

In this position, for example at take-ofi' and during the climb-outphase, the silencer elements 13 are deployed (at in order to projectinto the primary jet with a negative incidence a. They thus tap off orpeel off a certain fraction of said jet which they deflect in the mannerof scoops, into the annular space 12. The process of mixing between thegas of the jet and the secondary air flowing through the space 12 isconsequently vigorously promoted, this, as those skilled in the art willbe aware, leading to the creation of a particularly marked silencingeffect.

In the inoperative position, for example during cruising, the silenceelements 13 and their holder elements are fully retracted into cut-outs7a formed in the wall of the divergent portion 7, the continuity ofwhich is thereby re-established so that no loss of thrust occurs.

As stated hereinbefore, due to the fact that, in the operative positionthey have a negative incidence in the jet, the silencer elements 13 aresubjected to a resultant thrust R which tends to force them stillfurther into the body of the jet. The result is that considerable forcesare transmitted to the control or actuating devices (in particular thejacks 19) associated with these silencer elements. Keeping theseelements in their operative position, and returning them to theinoperative position, thus require the exertion of considerable forces,and this constitutes a drawback both from the engineering point of viewand from the economic point of view, a drawback which the presentinvention seeks to overcome.

In FIGS. 2 to 7, a dual-flow nozzle equipped with an improveddeflector-type silencer in accordance with a first embodiment of theinvention, has been illustrated. In particular, in FIGS. 2 and 20, therecan be seen the secondary fairing 3 including its divergent portion 7,as well as the boundary ll of the primary jet. As before, said fairingdelimits, between its internal wall and its external wall, a fixed boxor structure casing 10.

Uniformly distributed around the jet (see FIG. 3), and numbering 10 forexample, are the silencer elements which comprises deflectors or scoops31 carried by holder elements 32, which scoops can either occupy anoperative position (see FIG. 2) in which they project into the jet witha negative angle of incidence a, for example of the order of 20, or aninoperative position (see FIG. 2a) in which they are retracted, alongwith their holder elements, into the secondary fairing 3. Each silencerelement 31 has a free upstream edge and a free downstream edge,considered in relation to the direction of the gas flow. In theoperative position, said upstream edge is disposed nearer the centerline of the jet then is said downstream edge.

As before, cut-outs 7a formed in the divergent wall portion 7 andmatching the contour of the silencer elements 31, are closed ofi whensaid elements are in the inoperative position, thus re-establishingcontinuity in said wall. Said cut-outs can advantageously comprise, atleast at their upstream ends, a stepped-back edge 700 against which acorresponding edge of the relevant silencer element can seat.

Yokes 33, equal in number to the number of silencer elements 31 and eachcomprising two flanges fastened at 33a, 33b, 33c to the secondaryfairing, form a fixed reference structure.

The holder or supporting element 32 of the silencer element 31 isconstituted by a triangular-section arm (see FIG. 6) hingedly connectedat one of its ends to the yoke 33 through a pivot axis A mounted betweenthe two flanges of said yoke.

The silencer element 31 is constituted by a substantially rectangularplate having two opposite faces, namely a face 314 disposed towards theinterior of the jet and a face 31b disposed towards the exterior andexhibiting two ribs 310 (see FIG. 4). As FIGS. 2, 4 and 7 show, the saidsilencer element is arranged to pivot on its holder element 32 about apivot B carried by the ribs 310. At its ends adjacent the element 31 theholder element 32 has a portion 32a serving as a stop and designed tocooperate with a mating stop formation 31d carried by the upstream partof the external face 31b of said silencer element, in order thus tolimit in one direction the pivoting motion of the silencer element 31about the axis 8. At an intermediate point on the holder element orsupporting arm 32, there are articulared, by one of their ends in eachcase and about a pivot C, two links 34 which are disposed parallel toone another at either side of the holder element 32.

At their respective other ends, these links are articulated about apivot D to one of the ends of a lever 35 which is wide and short inshape, the lever itself being articulated at its other end to a pivot Ecarried by the two flanges of the aforesaid yoke 33.

The links 34 on the one hand, and the lever 35, on the other, constitutethe two articulated sections of a toggle mechanism designed in order tooccupy its deadpoint position when the silencer element 31 is in itsoperative position. In this position, the two sections of the togglelever mechanism are disposed in extension of one another (see FIG. 2).

Each of the assemblies constituted by a silencer element 31, its holderelement 32, its toggle mechanism 34, 35 and its control or actuatingarrangement 36, 37, forms an independent group. Instead of two smalljacks 37, it would be equally possible to employ a single jack of largersize.

When the silencer element or scoop 31 projects into the jet, itexperiences a resultant thrust R which is exerted at its center ofpressure P. An important feature of the invention resides in the choiceof the position of the pivot axis 8 in relation to said center ofpressure.

In FIGS. 2 and 4, it can be seen that the axis B divides the silencerelement 31 into an upstream section 31, and a downstream section 31,,and that the location of said axis is selected so that the center ofpressure P is contained in said downstream sections 31;, substantiallydownstream, in fact, of the axis B. Under these circumstances, if wecall R and R, the pressure forces respectively exerted at the centers ofpressure P, and P, of the upstream 31, and downstream 31, sections ofthe silencer element 31, and L, and L, the distances respectivelyseparating said centers of pressure from the axis B, then it will beseen that the relationship R,L, R L is applicable. The moment of theforce R, exerted upon the downstream section 31, of the silencer element31 thus predominates, so that said element tends to rotate about theaxis B in a direction such as to reduce its angle of incidence a in thejet, said angle being considered in terms of absolute value. Inaddition, by virtue of its drag component, the resultant force R alsoexerts a torque tending to rotate the assembly 31, 32 in the downstreamdirection about the axis A.

Let us now consider the behavior of the assembly 31, 32 and its controlarrangement, assuming first of all that the silencer elements 31 are tobe moved from their inoperative position into their operative position.The jacks 37 having been actuated in such a manner as to retract theirrods 36, the holder element 32, which is attached to said rods throughthe medium of the lever 35 and the links 34, rotates in the downstreamdirection about the axis A, aided in this movement by the aforesaid dragcomponent. It arrives in the final position when the links 34 aredisposed in extension of the lever 35. The toggle mechanism 34, 35 isthen in its deadpoint position and the holder clement held by the links34 and the lever 35 which operate in tension between the pivots E and C.The two jacks 37, whose piston rods have been retracted, therefore donot have to apply any force in order to maintain the assembly 31 32 inits operative position.

At the same time, the silencer element 31 automatically rotates, as wehave seen from the foregoing, about its axis B, until its stop 31d comesinto contact with the stop 32a fixed to the mounting 32. It will beobserved that this stop 32a is angled so that the negative angle ofincidence a finally adopted by the silencer element is conductive to theproduction of the desired "peeling effect. The assembly 31, 32 thenoccupies its operative position, as indicated by the reference I in FIG.2.

During the reverse maneuver, the jacks 37 are actuated so that theirrods 36 extend and the lever 35 pivots in the upstream direction aboutthe fixed axis E. The axes F and D describe circular arcs centered on E.The holder element 32 likewise pivots in the upstream direction aboutthe axis A, under the pull of the links 34.

At the start of this movement, the silencer element 31 remains at restagainst its stop 32a until it has reached the position [I (see FIG. 2)such that its lift in the jet is zero.

The intermediate position III is a later position in which the silencerelement 31, still located within the body of the jet, is no longeragainst the stop but instead can pivot freely. It then aligns itselfwith the jet streamlines and, consequently, remains in a position ofsubstantially zero lifi so that the force which the jacks 37 have toexert is substantially reduced.

FIG. 2a illustrates the final retracted position. The piston rods 36 ofthe jacks 37 have reached full extension while the lever 35, the links34 and the holder element 32 have been retracted in the upstreamdirection into the interior of the box structure 10. Shortly before thishappens, the upstream edge of the silencer element 31, which can tiltfreely, will have come into contact with the stepped-back edge 7a: ofthe cut-out 7a in the divergent portion 7. The downstream edge of thesilencer element seats against the flanges of the yoke 33 but couldequally seat against a rear edge similar to the stepped edge 7.124 ofthe cut-out in the divergent portion. The silencer element 31 thusrestores continuity to the wall of the divergent portion, for unsilencedflight.

It will be observed that unlike the known device shown in FIG. 1, inwhich the entry of the silencer element 13 into the jet, and its exittherefrom, are effected with the upstream end of said element, saidentry and exit take place, in the case of the silencer element of thepresent invention, with the downstream end of the element.

Summarizing, in the position 1 shown in FIG. 2, the force on the jacks37 is zero because the silencer element 31 merely exerts a tractiveeffort on the elements 34 and 35 secured to the fixed pivot axis E.Between the positions I and II, this force remains small because of theprogressive movement of said silencer element into a low-lift attitude.Finally, beyond the position II, the silencer element remains in thefeathered attitude (and thus in a zero lift position) until its finalretraction into the wall of the divergent portion 7.

Thus the silencer element 31, which is subjected in the jet to asubstantial force, can be operated by means of a low-power controlsystem which is therefore lighter, less bulky and less expensive thatthat necessary heretofore. It will be observed, in particular, that thelongitudinal and circumferential dimensions of this control system aresubstantially equal to those of the silencer element and that ittherefore leaves a substantial amount of space available for otherdevices which may be required.

ln FIGS. 8 to 12, a dual-flow nozzle equipped with a deflector or scoopsilencer in accordance with a second embodiment of the invention, hasbeen illustrated.

The silencer elements have been marked by the reference 101. Each ofthem is carried by a holder element 102 comprising two hollow parallelarms 102a, 102k attached together at one of their ends in each instanceby a hollow sleeve 102C and terminating at their other ends in eachinstance in a yoke l02aa, 102ba.

Each of the holder elements 102 is articulated about a geometric axis Ato a fixed reference structure comprising, in equal number to the numberof said holder elements, yokes whose flanges are constituted bylongitudinal sections 1030, 103b provided with peripheral ribs andapertured webs. These sections are positioned at the front by centringspigots 103m, l03ba, engaging in locations 104 integral with thesecondary fairing 3. They are fixed at the rear by pivots W carried byyokes 105 which are likewise integral with said fairing. Their spacingis maintained at the rear end by spacers 106 fixed by screws 107 (seeFIG.

Physical means defining the geometric axes A exists in the form of twobearings 108a, 10Gb (see FIGS. 10 and 12) respectively carried by thesections 103a and 103b, in which the hollow sleeve 102a is journalled.Said sleeve carries at its central zone two flanges constituting a yoke1024 holding a pivot F for the end of the rod 109 of a control oractuating jack 110. It will be observed that the sleeve 1020 isextended, beyond the bearing 108a in the form of a cantilever stub102cc, fixed to said sleeve, by welding for example.

In FIG. 9, the references 1100, 110b have been used to indicate thedelivery and return lines carrying the fluid to and from the jack.

Associated with each mounting 102 is a jack 110 arranged between thesections 103a, 103b, whose cylinder is hingedly connected through ajoint 11 1 to a crosspiece 112 itself pivotally assembled through twojournals 1 12a, 1 12b in bearings formed in said sections.

Each of the silencer elements 101, is equipped, on that of its facesdisposed towards the exterior of the jet 11, with two ribs 1010respectively articulated about a pivot axis B to the terminal yokes10204, 102%, of the arms 1020, 102b. At that of its ends adjacent therib 1010, each of the arms has a portion 102ab, l02bb doing duty as astop which cooperates with a mating stop 101d carried by the rib 1011:.

As in the embodiment hereinbefore described, the position of the axis Bis so chosen, in relation to the position of the center of pressure ofthe jet of the silencer elements 101, that said silencer elements pivotabout said axes and align themselves with the jet streamlines, that isto say in a position of substantially zero lift in which the forceexerted by the jacks 110 is substantially reduced, said pivoting motionbeing limited however, when the silencer is in the operativeconfiguration, by contact between the portions 101d on the ribs, and theportions 1020b, l02bb on the supporting arms 102a, 1021) (see FIG. 8a).

Associated with each silencer element 101, is a safety device comprisingmeans for elastically biasing said element towards its inoperativeposition, as shown in FIGS. 8 and 11.

Said safety device, visible in particular in FIGS. 10 to 12, comprisesmore specifically a torsion spring, which is preferably formed by asection of metal cable extending coaxially to the pivot axis A of theholder element 102, inside a sheath formed by the sleeve 102e, itsextension 1020a and an auxiliary sleeve 121. The latter has a flange 122coaxial with the bearing 108b, through which said auxiliary sleeve canbe attached to the section 103b using bolts 123. The flange 122 is cutaway (see FIG. 10), in order not to interfere with the positioning ofthe screws 10']. The internal bore of the sleeves 102e, 102m and 121, isin each case of circular cylindrical section, except at the respectivefree ends of the sleeves 1020a and 121, where locations 124, ofpolygonal sections, for example square, are formed which are smallerthan the cylindrical section.

The cable section 120 has two polygonal tips 120a, 1201: designed to fitin the aforementioned locations. With the sleeve 121 dismantled, thecable section 120 is engaged in the bore in the sleeves 102e, 102m, thetip 120a fitting in the location 124 in such a fashion that it slightlyprojects. The sleeve 121 is then passed over the cable section 120. Thetip 120b subsequently enters its location 125 where it likewise slightlyprojects. Finally, the flange 122 is fixed to the section l03b by thebolts 123.

One of the ends of the cable section 120 is thus secured to the holdingelement 102 whilst the other is 9 secured to the section 1031) whichforms part of the reference structure 103a, l03b.

The cable section 120 has a circular section which is smaller than thatof the bore in the sleeves so that it can, in consequence, twist freely.Its total length is slightly longer that that of the assembly of thethree sleeves in order to take account of the reduction in length whichoccurs with torsional loading. It will be observed in this context thatthe use of a cable section as a torsion spring is to be preferred to theuse of a torsion bar. As those skilled in the art will appreciate forthe same stress, a flexible cable experiences a larger angulardeflection. in addition, the risk of rupture of a cable is less thanthat which is present in a torsion bar, in view of the fact that anincipient crack in a strand ultimately simply means the failure of theparticular strand involved and not of the whole cable.

The relative angular positions of the two tips is chosen in such a waythat when the silencer element 101 is in its inoperative position, aresidual torsional torque remains which tends to keep the silencerelement in this position.

In operation, when the silencer is actuated, each silencer element 101,is introduced into the jet under the action of its control or actuatingjack 110. The sleeves 1021:, 1020a then rotate about the axis A inrelation to the sleeve 121 which remains fixed. The cable I20 whose tips120a, [20b are respectively secured to the pivoting sleeve 1200a and thefixed sleeve 121, is thus subjected to pure torsional loading anddistorts elastically, thus accumulating a certain potential energy. itwill be observed that because of the articulated assembly of thesilencer element 101 on its holder element 102, the thrust exerted bythe jet on this silencer element (said thrust in all cases tending toplace said element in its operative position) is small. The jack 1 10assembled in the yoke 102d therefore simply has to furnish the forcerequired elastically to twist the cable 120.

When the silencer is no longer required, the jack 110, by exerting athrust on the yoke 102d, cooperates with the cable 120 to return thesilencer element 101 to its inoperative position.

As we have seen, the energy required for this purpose is likewise lowbecause the silencer element 101 is rapidly placed in the zero liftposition.

The cable 120 thus restores the energy which it has stored during theprevious maneuver. In order to attenuate the shock occurring when thesilencer element 10] comes up against its stop in the retracted positionin the cut-out 7a formed in the divergent nozzle portion, a one-wayrestrictor 1100 can be arranged in the discharge line 11% of the jack inorder to throttle the discharge of fluid from the jack, thus to make itoperate as a damper.

In normal operation, the power of the jack 110 and that of the torsioncable 120 complement one another to return the silencer element 101, 102to its inoperative position. If the connection between the jack I10 andthe holder element 102 should fail, or if there should be a failure inthat part of the supply to the jack which is responsible for placing thesilencer element 101 in the operative position in the jet, the cable120, to which has been imparted an initial elastic torsion, maintainsthe silencer element 101 in its inoperative position.

In the event of a failure to that side of the jack supply responsiblefor placing the silencer element 101 in the inoperative position, thetorsion cable 120 on its own returns the silencer element 101 to saidinoperative position.

in the event of rupture of the cable 120, the jack on its own returnsthe silencer 101 element to its inoperative position.

Thus, extremely reliable dual control, operative to return the silencerelements to the retracted position, is obtained. The risk of unwantedjamming of the silencer elements 101 in the jet as a consequence of somekind of fault in their control arrangements, this being a situationwhich could give rise to substantial drag losses, is accordingsubstantially eliminated. This favorable factor can thus be taken intoaccount in planning the aircraft fuel consumption for a flight.

From the operating point of view, the silencer element 101, its holderelement 102, its control jack 110 and its elastic biasing device 120,are grouped in a selfcontained unit, with the exception of the jacksupply. This unit is readily accessible from the exterior of thedivergent portion 7 and is therefore easy to maintain.

it will be appreciated that the embodiments described are merelyexamples and are open to modifcation in various ways without in so doingdeparting from the scope of the invention as defined by the appendedclaims. We claim: 1. A silencer device for damping the noise produced bya gas jet escaping from a duct, comprising:

a fixed structure; a plurality of silencer elements distributed aboutsaid jet, each such element having a free upstream edge and a freedownstream edge relative to the direction of the gas jet; control meansfor moving each of said silencer elements between an operative silencingposition in which said silencer element projects with negative incidenceinto said jet in the manner of a scoop with said free upstream edgedisposed nearer the center line of the jet than is said downstream edge,and an inoperative retracted position, said control means including, foreach of said silencer elements: supporting means for supporting saidelement in said positions mounted for movement with respect to saidfixed structure and carrying the silencer element pivotable thereonabout an axis located intermediate the free edges of said element withthe center of pressure of the jet impinging on the element at a pointdownstream of said axis, whereby in use the silencer element issubjected to a pressure thrust tending to pivot it about said axis in adirection to reduce said negative angle of incidence in the jet, saidsupporting means including stop means thereon for engaging a cooperatingstop portion on the silencer element, thereby to limit the pivotalmotion of said silencer element about said axis in said direction anddetermine the incidence angle of said element when in its projectedoperative position; and

actuating means for moving said support means with respect to said fixedstructure and thus move said silencer element between its operative andinoperative positions.

2. A silencer device as claimed in claim 1 wherein said control meansfurther include spring means for biasing said silencer element at leastpartially away from its projected operative position.

3. A silencer device as claimed in claim 2 wherein said spring meansbiases said silencer element at least to a position at which said stopmeans and cooperating stop portion are out of engagement and saidelement is free to assume a position of neutral incidence in said jet.

4. A silencer device as claimed in claim 1 wherein said support means ishingedly connected to said fixed structure, and said actuating meansincludes a toggle lever comprising two lever arms which are articulatedat one end to each other and at the other end respectively to said fixedstructure and said support means, said toggle lever having its arms inaligned extended relation when said supporting means supports saidsilencer element in its projected operative position.

5. A silencer device for damping the noise produced by a gas jetescaping from a duct, comprising:

a fixed structure;

a plurality of silencer elements distributed about said actuating meansfor moving each of said silencer elements with respect to said fixedstructure between an operative silencing position in which it projectsinto said jet and an inoperative retracted position; and

spring means for biasing said silencer element at least partially awayfrom its operative projected position in the event of failure of saidactuating means.

6. A silencer device as claimed in claim 5 in which each of saidsilencer elements is carried by a supporting means hingedly connected tosaid fixed structure through a pivot axis, and said spring meansincludes an element which experiences torsion stress around said pivotaxis.

7. A silencer device as claimed in claim 5 wherein each silencer elementin its projected operative position is disposed with negative incidencein said jet in the manner of a scoop with its free upstream edgeextending nearer the center line of the jet than its free downstreamedge.

8. A silencer device as claimed in claim 7 wherein said spring meansbiases said element at least to a position in which said element hassubstantially neutral incidence in said jet.

9. A silencer device as claimed in claim 5 wherein said actuating meanscomprises a fluid-operated jack, said jack being provided withrestrictor means adapted to throttle the discharge of fluid from thejack when the silencer element is moved from its operative position intoits operative position.

10. A silencer device for damping the noise produced by a gas jetescaping from a duct, comprising:

a plurality of silencer elements distributed about said control meansfor moving each of said silencer elements between an operative silencingposition in which it projects into said jet and an inoperative retractedposition, said control means including, for each of said silencerelements:

supporting means carrying said silencer element and being hingedlyconnected to said fixed structure throu a pivot axis: actuating means rmovmg said supporting means 5 with respect to said fixed structure tothereby move said silencer element between its operative and inoperativepositions: and spring means for biasing said silencer element at leastpartially away from its operative projected position including a torsionspring coaxially mounted about said pivot axis with one end secured tosaid fixed structure and the other end secured to said supporting means.1 l. A silencer device as claimed in claim 10 wherein said torsionspring comprises a cable section.

12. A silencer device as claimed in claim 10, wherein said supportingmeans includes a hollow sleeve portion mounted coaxially about saidpivot axis, and said torsion spring extends inside said sleeve and hasone of its ends secured to said sleeve.

13. A silencer device as claimed in claim 12 wherein said fixedstructure comprises a hollow auxiliary sleeve mounted coaxially aboutsaid pivot axis as an extension of said first sleeve, and said torsionspring likewise extends inside said auxiliary sleeve and has its otherend secured thereto.

14. A silencer device as claimed in claim 13 wherein the internalsurface of at least one of said sleeves is of circular cross-sectionover part at least of the length thereof and includes a portion ofpolygonal section for engagement with correspondingly shaped tip at oneend of the torsion spring.

15. A silencer device for damping the noise produced by a gas jetescaping from a duct, comprising:

a fixed structure; a plurality of silencer elements distributed aboutsaid jet, said silencer elements having each a free upstream edge and afree downstream edge relative to the direction of the gas jet; controlmeans for moving each of said silencer elements between an operativesilencing position in which said silencer element projects with negativeincidence into said jet in the manner of a scoop and in which said freeupstream edge is disposed nearer the center line of the jet than is saiddownstream edge, and an inoperative retracted position, said controlmeans including, for each of said silencer elements: supporting meanscarrying said silencer element and hingedly connected to said fixedstructure; and

actuating means for moving said supporting means with respect to saidfixed structure to thereby move said silencer element between itsoperative and inoperative positions, said actuating means including atoggle lever comprising two lever arms which are articulated at one endto each other and at the other end respectively to said fixed structureand to said supporting means, said toggle lever having its arms inaligned extended position when said supporting means supports saidsilencer element in its operative projected position.

* t F i UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3 687 222 Dated August 29 1972 Inventor) Andre Alphonse Mederic LeonCAMBOULIVES et al It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 11, Claim 10, between lines 57 and 58, insert a fixed structure;

Signed and sealed this 23rd day of January 1973.

(SEAL) Attest:

ROBERT GOTTSCHALK Attesting Officer USCOMM-DC 6037B-P59 FORM PO-\O5O(10-69] u.s. GOVERNMENT PRINTING OFFICE 1949 o-3ss-3s4

1. A silencer device for damping the noise produced by a gas jetescaping from a duct, comprising: a fixed structure; a plurality ofsilencer elements distributed about said jet, each such element having afree upstream edge and a free downstream edge relative to the directionof the gas jet; control means for moving each of said silencer elementsbetween an operative silencing position in which said silencer elementprojects with negative incidence into said jet in the manner of a scoopwith said free upstream edge disposed nearer the center line of the jetthan is said downstream edge, and an inoperative retracted position,said control means including, for each of said silencer elements:supporting means for supporting said element in said positions mountedfor movement with respect to said fixed structure and carrying thesilencer element pivotable thereon about an axis located intermediatethe free edges of said element with the center of pressure of the jetimpinging on the element at a point downstream of said axis, whereby inuse the silencer element is subjected to a pressure thrust tending topivot it about said axis in a direction to reduce said negative angle ofincidence in the jet, said supporting means including stop means thereonfor engaging a cooperating stop portion on the silencer element, therebyto limit the pivotal motion of said silencer element about said axis insaid direction and determine the incidence angle of said element when inits projected operative position; and actuating means for moving saidsupport means with respect to said fixed structure and thus move saidsilencer element between its operative and inoperative positions.
 2. Asilencer device as claimed in claim 1 wherein said control means furtherinclude spring means for biasing said silencer element at leastpartially away from its projected operative position.
 3. A silencerdevice as claimed in clAim 2 wherein said spring means biases saidsilencer element at least to a position at which said stop means andcooperating stop portion are out of engagement and said element is freeto assume a position of neutral incidence in said jet.
 4. A silencerdevice as claimed in claim 1 wherein said support means is hingedlyconnected to said fixed structure, and said actuating means includes atoggle lever comprising two lever arms which are articulated at one endto each other and at the other end respectively to said fixed structureand said support means, said toggle lever having its arms in alignedextended relation when said supporting means supports said silencerelement in its projected operative position.
 5. A silencer device fordamping the noise produced by a gas jet escaping from a duct,comprising: a fixed structure; a plurality of silencer elementsdistributed about said jet; actuating means for moving each of saidsilencer elements with respect to said fixed structure between anoperative silencing position in which it projects into said jet and aninoperative retracted position; and spring means for biasing saidsilencer element at least partially away from its operative projectedposition in the event of failure of said actuating means.
 6. A silencerdevice as claimed in claim 5 in which each of said silencer elements iscarried by a supporting means hingedly connected to said fixed structurethrough a pivot axis, and said spring means includes an element whichexperiences torsion stress around said pivot axis.
 7. A silencer deviceas claimed in claim 5 wherein each silencer element in its projectedoperative position is disposed with negative incidence in said jet inthe manner of a scoop with its free upstream edge extending nearer thecenter line of the jet than its free downstream edge.
 8. A silencerdevice as claimed in claim 7 wherein said spring means biases saidelement at least to a position in which said element has substantiallyneutral incidence in said jet.
 9. A silencer device as claimed in claim5 wherein said actuating means comprises a fluid-operated jack, saidjack being provided with restrictor means adapted to throttle thedischarge of fluid from the jack when the silencer element is moved fromits operative position into its operative position.
 10. A silencerdevice for damping the noise produced by a gas jet escaping from a duct,comprising: a fixed structure; a plurality of silencer elementsdistributed about said jet; control means for moving each of saidsilencer elements between an operative silencing position in which itprojects into said jet and an inoperative retracted position, saidcontrol means including, for each of said silencer elements: supportingmeans carrying said silencer element and being hingedly connected tosaid fixed structure through a pivot axis: actuating means for movingsaid supporting means with respect to said fixed structure to therebymove said silencer element between its operative and inoperativepositions: and spring means for biasing said silencer element at leastpartially away from its operative projected position including a torsionspring coaxially mounted about said pivot axis with one end secured tosaid fixed structure and the other end secured to said supporting means.11. A silencer device as claimed in claim 10 wherein said torsion springcomprises a cable section.
 12. A silencer device as claimed in claim 10,wherein said supporting means includes a hollow sleeve portion mountedcoaxially about said pivot axis, and said torsion spring extends insidesaid sleeve and has one of its ends secured to said sleeve.
 13. Asilencer device as claimed in claim 12 wherein said fixed structurecomprises a hollow auxiliary sleeve mounted coaxially about said pivotaxis as an extension of said first sleeve, and said torsion springlikewise extends inside said auxiliary sleeve and has its other endsecured thereto.
 14. A silencer devicE as claimed in claim 13 whereinthe internal surface of at least one of said sleeves is of circularcross-section over part at least of the length thereof and includes aportion of polygonal section for engagement with correspondingly shapedtip at one end of the torsion spring.
 15. A silencer device for dampingthe noise produced by a gas jet escaping from a duct, comprising: afixed structure; a plurality of silencer elements distributed about saidjet, said silencer elements having each a free upstream edge and a freedownstream edge relative to the direction of the gas jet; control meansfor moving each of said silencer elements between an operative silencingposition in which said silencer element projects with negative incidenceinto said jet in the manner of a scoop and in which said free upstreamedge is disposed nearer the center line of the jet than is saiddownstream edge, and an inoperative retracted position, said controlmeans including, for each of said silencer elements: supporting meanscarrying said silencer element and hingedly connected to said fixedstructure; and actuating means for moving said supporting means withrespect to said fixed structure to thereby move said silencer elementbetween its operative and inoperative positions, said actuating meansincluding a toggle lever comprising two lever arms which are articulatedat one end to each other and at the other end respectively to said fixedstructure and to said supporting means, said toggle lever having itsarms in aligned extended position when said supporting means supportssaid silencer element in its operative projected position.